Methods and apparatus for image projection

ABSTRACT

Method and apparatus for a multi-application, laser-array-based image system utilizes three linear laser arrays. Each linear array generates multiple (N&gt;1) parallel output beamlets at one of the three primary colors (red, green, blue). The corresponding 1 to N output beamlets of the three linear arrays, each individually modulated in luminance according to a specific encoding scheme representing the video image to be produced on the viewing screen, are combined spatially to form a single white light linear array source. Through a projection/scanner optical system, the N output beamlets of the white light source are simultaneously directed to, and swept horizontally across a distant viewing screen, resulting in a swath of N lines of a graphic video image. By producing M contiguous swaths vertically down the viewing screen, a full image of M×N lines is produced. The red, green, and blue linear laser arrays may consist of arrays of semiconductor laser diodes made of suitable semiconductor materials so as to directly emit radiation at wavelengths corresponding to red, green, and blue colors, respectively. Alternatively, the red, green and blue color arrays may be formed by arrays of semiconductor laser diodes emitting radiation at twice the desired red, green and blue wavelengths, whose radiation is coupled to arrays of second harmonic generation crystal elements.

This is a continuation of application Ser. No. 08/13,036 filed of Feb.3, 1993 now abandoned.

BACKGROUND OF THE INVENTION

This invention relates generally to a high resolution, image projectionsystem employing at least one linear array of laser sources, suitablefor displaying raster scanned monochrome, two color and full colorimages such as television video or computer generated text and graphicsby projection onto a screen.

Conventional cathode ray tube (CRT) display devices become impracticalfor large screen sizes. The largest CRT consumer TV display generallydoes not exceed 40 inches measured diagonally across the screen.

For graphics image display, the ability of the CRT within a monitor toproduce a proportional number of pixels for a unit screen area decreasesas the tube size gets larger. This limits the ability of larger CRTs toproduce the fine detail needed in graphics displays viewed at closedistances. This occurs because of the difficulty in accuratelyreproducing the super fine red, green, and blue (RGB) phosphor trios orstripes over a larger face area without error during the manufacturingprocess. Furthermore, errors introduced in the deflection of theelectron beam are magnified by the distances associated with the largertube and cause spatial distortion of the pixel information on thescreen.

In contrast to graphics displays, consumer TV displays must be brightand have high contrast. Since consumer TV displays are viewed at muchgreater distances than graphics displays, resolution is not anoverriding factor. Additionally, CRTs generate low frequencyelectromagnetic fields and X-rays. Methods that are used to achieve highbrightness cause the electron beam spot size to increase dramatically.As a consequence, this larger spot size causes a large reduction inimage sharpness, that in turn reduces contrast and results in softlooking images. Additionally, larger TV screens require a largerdeflection angle to prevent the CRT from becoming excessively long.Large deflection angles (over 90 degrees), coupled with large screensize, cause noticeable errors in linearity and color purity. Moderntelevision CRTs were never intended to be large. The size, weight, andpower trade-offs do not scale economically for large CRT systems.

As a result, video projectors using superposition of three CRT lightsources for the primary colors of white light, namely red, green, blue(RGB), are commonly used. A standard product configuration uses threesmall diameter primary color CRTs and lenses to converge three separatecolors at a screen image. Larger projection screen sizes, than thoseobtainable using a CRT, can be obtained using this method; however, thebrightness and contrast are poor compared to that of a CRT used for homeTV video viewing.

Another approach uses a single incandescent white light source togenerate the primary colors that illuminate a LCD panel(s). The RGBpixels are independently modulated by the liquid crystal display ("LCD")selection matrices, that also generate the rastering. Although theseprojectors have fair resolution, there are other unavoidable problemsrelated to this scheme. The incandescent white light source has arelatively short operating life and generates relatively large amountsof heat. The LCD devices cannot be manufactured without some minimumnumber of defects that, in turn, manifest themselves as permanent imageartifacts on the screen regardless of the graphic or video source. UsingLCD devices to generate the raster introduces a fixed and permanentresolution to the display device, making it very difficult to adapt theelectronics to accept other resolutions for display of graphics and textinformation.

Brighter video projectors have been constructed using lasers. Typically,the green and blue beams are generated by argon ion gas lasers thatdirectly emit green and blue radiation; the red beam is usuallygenerated by a liquid dye laser (pumped with part of the high power blueand green gas lasers). Generally, each of the three light beams isindependently modulated to produce the same luminance and chrominancerepresented by an input video signal. The three modulated beams are thencombined spatially by optical means to produce a single so-called "whitelight" beam and directed toward the viewing screen by an appropriateraster/scanner optical system. Since only a single white light beam isprojected toward the viewing screen in present gas-laser-basedprojection systems, they are of the N=1 type, the number N specifyingthe number of white light beams. In such systems, generally, a fullcolor picture (or frame) is produced at the viewing screen by projectinga series of pixels using a combination of rotating and deflectionmirrors. With proper synchronization, the rotating mirror scans thewhite light beam horizontally across the screen, sequentially painting arow of pixels; the deflection mirror simultaneously moves the whitelight beam vertically down the screen, filling out the picture frame oneline of pixels at a time. At any given instant, the white light beamilluminates a given pixel in the frame with the appropriate luminanceand chrominance.

Present laser-based N=1 video projector systems are generally capable ofproducing a brighter image than non-laser based systems, and they canachieve close to 100% color saturation. They also exhibit pixel sizestability, since the pixel size is independent of white light beampower. In order to produce a reasonably bright image on a screen largerthan 40 inches, the white light beam power at the screen should be inexcess of three watts. Gas lasers used in present N=1 projection systemshave power efficiencies typically <0.1 percent; accordingly, present daygas-laser-based projection systems require several kilowatts ofconditioned electrical power and conditioned cooling water sufficient toremove several kilowatts of waste heat. Such systems are thereforerelatively big, lack easy portability and are expensive. In present N=1laser-based systems, three separate acousto-optic (AO) light modulatorsare used to impress video modulation information on each of the threeRGB beams that forms the single white light output beam. Thesemodulators are problematic and costly. At the power levels needed forbright large-screen displays, modulation nonlinearities and otherundesirable effects can degrade picture quality.

Associated with conventional laser-based video projectors has been theneed to use high speed components, both mechanical for scanning andelectronic for modulation in order to produce a standard televisionpicture. Current NTSC television pictures are reproduced at the rate of1/30th of a second per frame, with each frame being filled by 525horizontal scan lines. In a laser video projector, a multi-facet rightpolygon mirror is typically used for scanning the single white lightlaser beam across a screen. Even a 48-facet mirror would require anangular velocity in the region of 50,000 rpm. Bearings capable of suchperformance are very expensive. The scanning problem becomes even morecritical when dealing with High Definition Television (HDTV) or highresolution graphics, since the pixel density increases, therebyrequiring an even higher angular velocity of the polygon mirror.

Various video standards, such as NTSC, and variations of HDTV andcomputer standards already exist, and new standards will in time beproposed. Among other considerations, these video standards may differin resolution, picture aspect ratio, frame rate, and interlacing method.Therefore, it would be desirable to have an image projector capable of,or easily adapted to, displaying video pictures conforming to variousexisting or future video standards.

Thus, there is a tremendous need for a bright, low cost compact videoand graphic image projector capable of displaying multiple resolutionsof video pictures such as NTSC, HDTV, and high resolution graphicspictures. Furthermore, since the requirements for display of graphicsand TV video are different, it would be very desirable to combine thedisplay function of both types of images into a single portableprojection unit.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved method and apparatus for video and graphic image projection,capable of reproducing various video standards such as NTSC, HDTV,computer graphics, and other high resolution video pictures.

It is another object of the present invention to provide a low costmethod and apparatus for monochrome, two color and full color imageprojection that is amenable to mass production.

It is yet another object of the present invention to provide a methodand apparatus for image projection that is power efficient and compact.

It is a further object of the present invention to provide a laser whitelight source array that is amenable to mass production.

It is additional object of the present invention to provide a method andapparatus for image projection that uses an optical scanner withrelatively slow rotational speeds.

It is another object of the present invention to provide a method andapparatus for image projection system that uses pulse width modulationto generate a high contrast video image.

These and additional objects are accomplished by an improved imageprojection system comprising three major subsystems: 1) a laser-basedlinear-array white light source; 2) a system for formatting an inputvideo picture data suitable for digital two-dimensional processing; and3) an optical scanning/projection system for directing multiple beams ofa white light linear array source onto a distant viewing screen.

According to one aspect of the invention, a plurality (N>1) of paralleloutput beamlets of a laser-based linear array single color, two color orfull color (also referred to herein as "white light") source are scannedhorizontally across the screen by means of a rotating polygon mirror,illuminating the screen in a swath of N lines. An image resizingprocessor reformats input picture data into a form suitable for drivingRGB linear laser arrays that comprise the white light source. As part ofthe formatting process, the image resizing processor converts the inputpicture data into video frames. The optical scanning/projection systemdirects the N parallel output beamlets from the white light array sourceonto the screen to recreate the input picture or image by filling thescreen with illuminated pixels swath-by-swath, and frame-by-frame. Theentire image projection system is controlled by a system controlmicroprocessor which receives input from a video input converter andfrom either a local control panel or an external computer.

According to another aspect of the invention, the laser-based whitelight source is produced by spatially combining corresponding N paralleloutput beamlets of three primary color linear arrays, each of whichprovides N parallel output beamlets at the red, green, and bluewavelengths.

In one embodiment, the three primary color linear arrays and combiningoptics, including dichroic mirrors, are mounted on a common base plate.The primary color red, green and blue beams are produced by severaldifferent methods, and the respective N output beamlets are modulated byseveral different methods in several different information formats.

In another embodiment, each primary color linear array incorporates alinear array of N individually-addressable semiconductor stripe laserdiodes grown with a semiconductor material whose composition results inlaser diode emission at the desired red, green and blue wavelengths. Thelight intensity of each of the N parallel-directed output beamlets ismodulated by directly modulating the drive current supplied to each ofthe semiconductor stripe laser diodes. The N parallel-directed,modulated output beamlets of each primary color array are collimated byN corresponding micro-optic lenses contained in a linear lens array thatis mounted monolithically with its respective primary color laser diodearray.

In yet another embodiment, modulation is imposed on each of the Nparallel-directed output beamlets of each of the primary color arrays bypassing the beamlets through a corresponding optical coupling lens and acorresponding solid state electro-optic modulator. The coupling lensesand the solid state modulators are contained in linear arrays mountedmonolithically with the semiconductor laser diode array and outputcollimating lens array.

In another embodiment, each primary color linear array consists of alinear array of N individually-addressable semiconductor stripe laserdiodes emitting parallel beamlets at an infrared wavelength equal totwice the desired red, green, or blue wavelength. The infrared output ofeach such array is converted to an array of red, green, or blue outputbeamlets by passing each beamlet through a corresponding opticalcoupling lens and stripe waveguide made of an appropriate nonlinearcrystalline material. The N coupling lenses and nonlinear waveguides arecontained in a linear lens array and waveguide array, respectively,mounted monolithically with the semiconductor laser diode array andoutput collimating lens array. Image information modulates the Nparallel-directed output beamlets of each primary color array, either bydirectly modulating the drive current of the individual semiconductorstripe laser diodes in the array, or by incorporating an array of solidstate electro-optical modulators following the nonlinear waveguide arrayand prior to the output collimating lens array. In the alternative, ared beamlet may be directly generated by use of a suitable semiconductormaterial without the need for a nonlinear crystalline material harmonicgenerator.

According to another aspect of the invention, the video informationimpressed on the N beamlets of each of the three primary color arraysmay take several different forms.

In one embodiment, the modulation is implemented by modulating the drivecurrent of the individually addressable semiconductor stripe laserdiodes. This differs from acousto-optic modulation utilized inconventional (N=1) laser projector systems because semiconductor laserdiodes can be abruptly turned on and off at high rates. In the presentinvention, pulse width modulation ("PWM") is used without therequirement of prohibitive high-speed/high bandwidth electronics sincethe simultaneous scanning of N lines of the video image greatlyincreases the time available to scan a given swath across the screen ata given frame rate. Since N lines are processed in parallel, the dataprocessing rate is reduced by the factor N. For example, a PWM methodfor 2⁷ =128 grey levels may require an increase of data processing rateby a factor of 128. This increase can be offset if N=128 lines arescanned in parallel, since the time to process each pixel is thenreduced by a corresponding factor of N=128.

According to another aspect of the invention, the opticalscanning/projection system comprises a rotating polygon mirror withprogressively tilted facets (hereinafter also referred to as an"irregular polygon mirror") to scan the white light array outputhorizontally across the screen, to also raster the swath scan verticallydown the screen. The rotating polygon has at least as many facets, M, asthe number of swaths required to fill the picture frame. Starting from afirst facet, a first swath is "painted" across the top of the pictureframe. Each successive facet is progressively tilted so as to paint eachsuccessive swath directly below the preceding one and contiguous withit, until the picture frame is filled, whereupon the first facet onceagain begins to paint a swath at the top of the next frame. Since acomplete frame is painted using a tilted facet polygon mirror, nogalvanometer is required to raster each successive swath vertically downthe screen.

In another embodiment, the rotating polygon scan mirror has M facetswhose normals maintain a constant angle relative to the mirror spin axis(hereinafter also referred to as a "regular polygon mirror"). To rastereach successive swath vertically down the screen, a galvanometer isplaced between the rotating polygon scan mirror and the laser array.

An important feature of the present invention is the simultaneousparallel scanning of N pixel lines. As mentioned in connection with PWMabove, this parallel processing feature scales down the required speedof associated electronics. A similar mechanical advantage is also gainedfor the optical scanning/projection system.

In the present invention, each polygon mirror facet is employed to scana swath of N lines instead of a single line. For a given fixed frametime, the angular velocity (also referred to herein as "rotationalspeed") of the swath scan polygon mirror is reduced by a factor of Ncompared to that required for a single line scan polygon mirror. Forexample, if a swath of 128 lines is scanned, a 10-facet polygon mirroris required to scan and raster a picture frame of 1280 horizontal lines.By comparison, if only one line is scanned at a time (N=1, as inconventional laser projectors) a 10 facet polygon mirror turning at anangular velocity 128 times higher will be required.

In one embodiment, an interlace galvanometer is optionally employed intandem with the rotating polygon mirror having progressively angledfacets (an irregular polygon mirror). This rotating polygon mirror byitself will only produce a progressive (swath sequential) scan for eachpicture frame. In order to support interlaced video standards, anadditional deflection offset is required on alternating fields and isperformed by the interlace galvanometer. The interlace galvanometerperforms a minor shift to offset successive fields. For example, in a2:1 interlace, the shift amounts to half a horizontal line spacing forthe entire stream. A picture frame is then formed by interlacing twopartial frames of "fields", where a field rate is twice that of theframe rate.

In yet another embodiment, an interlace galvanometer is used togetherwith the combination of a regular polygon mirror and a galvanometerwhich rasters each successive swath vertically down the screen.

According to another aspect of the invention, by increasing the numberof N parallel-directed output beamlets to the desired number of rasterlines, the rotating polygon mirror and interlace galvanometer can beeliminated, thereby reducing noise vibration, heat and projection errorsattributable to the rotating mirror, its associated motor and drivingelectronics. In this embodiment a single mirror having a height at leastequal to the height of N lines is used to provide horizontal deflection.If desired, interlacing may be provided with a separate interlacegalvanometer.

According to another aspect of the invention, a data processing systemcomprises an image resizing processor and a frame storage unit. Theimage resizing processor transforms input picture data from varioustypes of video standards to a format suitable for the image projectionsystem of the invention. Essentially, the image projection system isdesigned with a preselected resolution. The image resizing processormaps a picture of a given video standard into the preselected resolutionof the image projection system (e.g., represents the picture by theconstant number of pixels of the laser projection system). The imageresizing processor maps a picture from a lower resolution video standardto that of a high resolution video standard.

The electronic remapping of pictures from various video standards into apreselected resolution system is an important feature of the presentinvention. Such remapping is implemented with a hardware acceleratorusing interpolation. Digital methods are superior to conventionaloptical methods, and greatly simplify the electronics of the imageprojection system for displaying pictures from the various videostandards having different resolutions, aspect ratios, and frame rates.

For example, the preferred embodiment of the present invention has aresolution defined by 1280×1280 pixels within a frame having a screenaspect ratio of 16:9. Pictures from many video standards can bedisplayed at that resolution. Thus, a HDTV picture will have the samescreen aspect ratio, and the image resizing module will essentially mapthe digitized input video source picture into the 1280×1280 pixels ofthe laser projection system.

When an NTSC picture is remapped, since the picture has a screen aspectratio of 4:3 (12/9), the active display picture will fall within acentral band flanked by left and right margins. The pixels in the leftand right margins (each occupying one-sixth of the horizontal dimension)will not be utilized. Thus, the picture is mapped by the image resizingprocessor onto the pixels (960×1280) in the central band.

Video standards with different vertical scan rates of frame rates areeasily accommodated by varying the angular velocity (rotational speed)of the polygon mirror. Accordingly, increasing the angular velocity ofthe polygon mirror speeds up the field and frame rates.

The invention provides an image projection system that is powerefficient, has high performance, is amenable to low-unit-costmass-manufacturing processes, and is compatible with multiple videostandards.

Additional objects, features, and advantages of the present inventionwill be understood from the following description of the preferredembodiments, a description which should be referenced in conjunctionwith the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram illustrating the color image projection systemof the present invention;

FIG. 2A illustrates the line-by-line raster scan of a conventionalsingle beam (N=1) imaging system, such as that of a CRT;

FIG. 2B illustrates the swath-by-swath raster scan of the color imageprojection system of the present invention;

FIG. 3A is a perspective view illustrating the use of a polygon mirrorhaving progressively tilted adjacent facets to project a first swath ofN lines.

FIG. 3B is a perspective view illustrating the use of a polygon mirrorhaving progressively tilted adjacent facets to project a second swath ofN lines.

FIG. 4 is a block diagram of a first alternative embodiment of theoptical scanning/projection system of FIG. 1;

FIG. 5 is a block diagram of a second alternative embodiment of theoptical scanning/projection system of FIG. 1;

FIG. 6A is a perspective view of a primary-color linear laser arraysource of the present invention;

FIG. 6B is an enlarged view of the area of FIG. 6A indicated by line6B--6B.

FIG. 6C is an enlarged view of the area of FIG. 6A indicated by the line6C--6C.

FIG. 7A illustrates a top plan view of an embodiment of the white lightlaser array source of FIG. 1;

FIG. 7B is a front plan view of the white light laser array source ofFIG. 7A.

FIGS. 7C and 7D are an enlarged view of the area of FIG. 7B indicated bythe line 7C--7C and 7D--7D.

FIGS. 8A through 8D are a diagram of an image projection system of thepresent invention detailing the data processing system of FIG. 1.

FIG. 9 is a diagram that illustrates a picture frame being mapped by theimage resizing module to another picture frame with the same aspectratio but with a higher resolution;

FIG. 10A specifies parameters for the display of the HDTV: SMPTE 240m(1125) standard.

FIG. 10B specifies parameters for the display of the proposed HDTV: 1050NBC standard.

FIG. 10C specifies parameters for the display of the NTSC: RS-170Astandard.

FIG. 10D specifies parameters for the display of the VGA(Monochrome/Color) standard.

FIG. 11 is a timing diagram that illustrates a pulse-width-modulationmethod according to one embodiment of the present invention.

FIG. 12 is a perspective schematic layout that illustrates in furtherdetail one embodiment of the optical scanning/projection system of FIG.1.

FIG. 13 is a perspective schematic layout that illustrates in furtherdetail a second embodiment of the optical scanning projection system ofFIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1 a color image projection system 10 is shown. Thecolor image projection system 10 includes a white light linear arraysource 100, a data processing system 200 for formatting input picture orimage data into a suitable form to modulate the white light linear laserarray source 100, and an optical scanning/projection system 300 forscanning and projecting the output beams of the white light linear laserarray source 100 onto a projection screen 400. The output beams of thewhite light linear laser array source 100 may also be projected onto orinto other photoreceptors such as an eye, paper, photosensitive film orother photosensitive materials.

The white light linear laser array source 100 produces a plurality N ofwhite light parallel-traveling beamlets 102. Each of the separatebeamlets is formed by spatially combining the N parallel-travelingoutput beamlets of each of three primary color linear array sources, ared linear array 104, a green linear array 106, and a blue linear array108. Each of the parallel-traveling linear array outputs of single colorN beamlets 110, 112 and 114 of the three primary color linear arraysources 104, 106 and 108, respectively, is then combined by combiningoptics 116, element-by-element, into a linear array of Nparallel-traveling white light beamlets 102. The term "white lightbeamlet" includes not only a white light appearance in its literalsense, but also includes colors produced by varying combinations of red,green and blue light intensities. The number of beamlets N is between 2and any integer power of 2 (inclusive).

As detailed further herein, the linear array of N parallel travelingoutput beamlets 102 is reflected and refracted by the opticalscanning/projection system 300 to simultaneously scan a swath of N linesacross the projection screen 400, and to raster M successive swath scansdown the projection screen 400. Thus, in contrast to the line byline-by-line raster scan of a conventional single beam CRT as shown inFIG. 2, the color image projection system 10 simultaneously scans aswath of N lines across the projection screen 400 as illustrated in FIG.3.

The data processing system 200 reformats an input video or graphicsignal 201 (hereinafter collectively referred to as "video") intoswaths, the total of which create a screen full of pixels. Each of theindependently addressable sets of beamlets 110, 112 and 114 of the threeprimary color linear array sources 104, 106 and 108, respectively, ismodulated accordingly, so that the combined N white light beamlets ofthe white light linear array source recreates the input picture byfilling the projection screen 400 with illuminated pixels,swath-by-swath, frame-by-frame.

The data processing system 200 includes a video input converter 202which converts common types of picture signals, such as composite video,analog RGB or computer graphics into digital Red, Green, Blue (RGB)data. Chip sets for performing such conversions are commerciallyavailable from the Signetics Division of Philips Semiconductors ofSunnyvale, California as further detailed herein with reference to FIG.8A.

In the preferred embodiment of the invention, a microprocessor-basedcontroller 204 in conjunction with a memory 206 is employed to controlthe video input converter 202 via a bus 208. In this way, the decodingand formatting of the video signal are under microprocessor control. Thebus 208 allows decoded timing information such as sample clock(horizontal sync) and frame reference to be passed to other portions ofthe color image projection system 10. In addition, the bus 208 may beutilized to transfer control information between an external computer orcontroller and the image projection system 10. For example, an externalhost computer connected to the bus 208 can be used to control the amountof hue, saturation, tint, and other composite NTSC attributes.

The video input converter 202 provides a red digital data stream 210, agreen digital data stream 212 and a blue digital data stream 214. Eachof the streams 110, 212 and 214 is a serial pixel stream 8-bit wide,that provides a grey scale of 2⁸ =256 levels for each color data stream.Each stream has a raster format that fills a frame line-by-line. Sincethe color image projection system 10 fills a frame with one or moreswaths of N lines, the single serial pixel stream needs to bereformatted into multiple (e.g. N) serial pixel streams, one for each ofthe N output beamlets of the white light linear array source 100. Stateddifferently, the digital data streams 210, 212 and 214 need to beconverted from a single beam raster scan format as shown in FIG. 2A toan N-beamlet raster scan format as shown in FIG. 3B. Since N can bequite large, for example 64, 128 or even higher, it is preferable tomultiplex the 8-bit parallel path for the grey scale pixel informationfor each of the N lines in the pixel stream. In the preferred embodimentof the invention, 8-bit grey scale pixel information is converted tomultiplex form by a set digital processors 216, 218 and 220. Forexample, the serial sequential pixel stream of digital Red data 210(8-bits wide represents all the first pixels in order from 1 to N for aswath, followed by all the second pixels of the swath, etc.) isprocessed by the digital processor 216 and emerges as a singlemultiplexed pixel stream. Similarly, the serial sequential pixel streamsof digital green data 212 and blue data 214 are processed by a digitalprocessor 218 and a digital processor 220, respectively.

The digital processors 216, 218 and 220 also serve to convert data froma selected video standard (e.g., resolution, aspect ratio) to that ofthe color image projection system 10 as detailed further herein,particularly with reference to FIGS. 8A through 10D. The imageprojection system 10, however, may be used without such data conversionwhen displaying an image format which matches or corresponds to thepreselected image format of the image projection system 10.

A multiplexed red pixel stream 222 from the digital processor 216 issubsequently used to modulate the corresponding individually-addressableoutput beamlets of the red linear array source 104. Similarly, the greenand blue multiplexed pixel streams 224 and 226, respectively, are usedto modulate the corresponding output beamlets of the green and bluelinear array sources, 106 and 108, respectively. In the preferredembodiment of the invention, such modulation is performed using apulse-width modulator (PWM) 228, for the red component. The pulse-widthmodulator 228 and its advantages are described in further detail withreference to FIG. 10. Similarly, a pulse width modulator 230 operates onthe green component, while a pulse width modulator 232 operates on theblue component.

After the white light linear array source 100 is modulated by a set ofN-pixel streams 234, 236 and 238, the emerging linear array of Nparallel-traveling traveling modulated white light beamlets 102 isoptically processed to produce, by way of the opticalscanning/projection system 300, a raster scan, having one or moreswaths, on the screen 400.

In one preferred embodiment of the invention, the opticalscanning/projection system 300 comprises a mirror 302 which is integralto a galvanometer 304, and rotating regular polygon mirror 306 which isdriven by a motor 308. The galvanometer 304 and the motor 308 are eachcontrolled by a raster generator servo 310. The rotating regular polygonmirror 306 has as at least many facets as the number of swaths Mrequired to generate the full picture frame. In further detail, startingfrom a first facet, a parallel traveling set of N beamlets 102 strikethe mirror 302. The beamlets 102 are reflected by the mirror 302,reflected again by the polygon mirror 306, then refracted by a set ofprojection optics 312 to thereby scan a first swath across the screen400, starting at the left top of the picture frame. This embodiment usesa 9 facet regular polygon mirror having a diameter of approximately 3inches. This results in a polygon scan efficiency of 0.675. The verticalscan efficiency is set by the performance capability of the galvanometerand the number of inactive facets during a field cycle. Inactive facetsare used to allow the galvanometer to retrace before starting a newfield. A reasonable scan efficiency for a galvanometer is in the 70%(less than 80%) range. Consequently, at least 3 inactive facets arerequired during a scan cycle with a corresponding galvanometer scanefficiency of 0,727 (8/8+3)). The resulting overall scan efficiency is0.49 (the product of 0.675 and 0,727) and the throughput efficiency ofthis system with a transmission of 0.60 would be less than 0.294 (theproduct of 0.60 and 0.49). The 9 facet/3 inch polygon system with a72.7% vertical scan efficiency requires a spin rate of 4400 RPM toproduce an 8 swath field at a 60 Hz field rate.

The net result is that a 128 element laser with a total power of 3.4Watts per laser diode array (26.6 mW per element) will provide 3 Wattsof power at the screen (the product of 3, 3.4 and 0.294).

An important feature of the invention is the use of angled facets toprovide vertical rastering. Conventional projection systems typicallyemploy a rotating regular polygon (the surface normals of all facetsbeing perpendicular to the rotational axis) for horizontal scanning, anda second rotating mirror (usually a galvanometer) to raster the beamvertically down the screen. This adds complexity and cost to the system.

In another preferred embodiment of the optical scanning/projectionsystem 300 as shown in FIG. 1, the galvanometer 304 with its integralmirror 302 is employed in tandem with the rotating irregular polygonmirror 306.

As detailed in FIGS. 3A and 3B, the surface normal to the second facetis tilted relative to the surface normal to the first facet to therebyindex the second swath scan vertically down the screen, so that thebottom horizontal line of the first swath scan is contiguous with thetop horizontal line of the second swath scan. The surface of eachsuccessive facet is similarly tilted with respect to the preceding facetto raster successive swath scans vertically down the screen until Mswath scans are made and the whole picture frame is filled, whereuponthe first facet once again begins to produce the next frame. One or morefacets (in excess of the number M) may be utilized in the polygon mirror306 to accommodate any vertical blanking interval signal included withinthe video signal 201.

The rotating irregular polygon mirror 306 by itself, however, will onlyproduce M contiguous swath scans for each picture frame. Thegalvanometer 304 and its integral mirror 302 provide interlaced swathsto thereby display interlaced video signals. The galvanometer 304produces a minor shift in the angle of the mirror 302 to thereby offsetsuccessive fields. For example, in a 2:1 interlace, the shift amounts tohalf a horizontal line spacing. In 2:1 interlaced systems, a pictureframe is formed by the eye integrating "fields", where the field rate isdouble that of the frame rate.

In this preferred embodiment of the invention as shown in FIG. 1, an 18°scan is used to minimize the swath mismatch error generated by thepyramidal tilt of the irregular polygon mirror facets. The nominal swathmismatch error for an 8 swath 18° scan with a 1.8:1 aspect ratio isapproximately ±1/5 of a line pitch. Limiting the effect of fabricationerrors in the pyramidal tilt to less than ±1/5 of a line pitch requirestolerances tighter than ±3 arc seconds. The dynamic errors of polygonwobble and facet to facet timing also require accuracies ofapproximately ±1 arc second to be negligible contributors to rasterimpairment. Swath mismatch and pyramidal error contribute a peak to peakerror of ±2/5 of a line pitch.

An 8 swath field requires an irregular polygon mirror with a multiple of8 facets. The scan efficiency for an 8 facet polygon mirror with ahorizontal scan of 18° and a diameter of approximately 2 inches is 0.2.To double the scan efficiency to 0.4 with a 16 facet polygon requires adiameter of approximately 6 inches. Such a diameter increase, however,increases the mass of the mirror by about fifty percent.

An important feature of the image projection system 10 of the presentinvention consists of the simultaneous scanning of N pixel lines of thepicture frame. This method greatly reduces the angular velocity of thepolygon mirror 306 required to fully illuminate a picture frame at aspecified frame rate. Each polygon mirror facet is employed to scanswath-by-swath instead of line-by-line. This reduces the product of thenumber of facets and the angular velocity by a factor equal to thenumber of lines N in the swath in contrast to an N=1 system. Forexample, if a swath of 128 lines is scanned at a time, a 10-facetpolygon mirror 306 needs to be employed to produce a picture frame of1280 horizontal lines. If desired, however, the polygon mirror 302together with an N=1white light source can be utilized to produce aframe having a number of lines equal to the number of successivelyangled reflective facets of the mirror 306 without the need for aseparate vertical deflection mirror.

Video standards with different vertical scan rates or frame rates areeasily accommodated by varying the angular velocity of the polygonmirror 306. This method provides a tremendous advantage overmagnetically deflected systems where scan rate changes requiredifferently configured yoke windings and compensation for the resultantchanges in yoke inductance. The raster generator servo 310 obtainstiming signals from the bus 208 and ensures that the mirror 306 turnsand that the mirror 302 is deflected at desired rates, both insynchronization with the raster scan.

Referring now to FIG. 4, a first alternative embodiment 500 of theoptical scanning/projection system 300 of FIG. 1 is shown. Inparticular, where the total number of lines to be projected for adesired frame is equal to N, the galvanometer 304 with its integralmirror 302, simply reflects the N lines of white light to thereby scanthe N lines across the screen 400. Unless required for interlacing, novertical rastering is necessary in this embodiment. This arrangementprovides a significant decrease in noise, vibration and heat whichresult from the motor 308 and the rotating polygon mirror 306. Inaddition, mismatch errors due solely to the polygon mirror 306 areeliminated.

Referring now to FIG. 5, a second alternative embodiment 600 of theoptical scanning/projection system 300 of FIG. 1 is shown. In the secondalternative embodiment 600, the polygon mirror 602 consists of a mirrorwhere the surfaces of each of its facets are parallel to the axis ofrotation of the mirror 602, in contrast to the mirror 502 utilized inFIG. 4.

In the embodiment shown in FIG. 5, where the desired number of lines tobe projected as a frame is equal to N, and no interlacing is required,no vertical rastering apparatus is necessary. However, if the desirednumber of scan lines in a frame is less than N, then the mirror 602, incombination with a galvanometer (not shown) for vertical detection wouldprovide the desired number of scan lines in a frame.

Thus, this third alternative embodiment would appear as that of theoptical scanning/projection system 300 at FIG. 1, except that thegalvanometer 304 and mirror 302 combination would be utilized to providevertical deflection instead of merely interlacing, and the polygonmirror 306 would provide only horizontal deflection since the facets ofthe polygon mirror are not tilted with respect to each other. With thisthird alternative embodiment of the optical scanning projection system,the angular velocity of the mirror 602 would be reduced by a factor of Nover systems where N=1.

White light Laser Linear Array Source

FIGS. 6A, 6B and 6C illustrate in detail the red laser array 104 ofFIG. 1. Except for the frequency of the light emitted from the array104, the array 104 may be utilized as the green laser array 106 and theblue laser array 108. Mounted in alignment on a base substrate 700are: 1) a monolithic linear array of individually-addressable stripesemiconductor laser diodes 702; 2) a linear array of micro-opticallenses 704; 3) a linear array of integrated electro-optic modulators706; 4) a linear array of micro-optical lenses 708; 5) a linear array ofnonlinear harmonic converters 710 and 6) a linear array of outputbeamlet collimation micro-optic lens 712. The monolithic linear array702 includes a set of N (e.g. 64, 128, . . . ) individually-addressable,semiconductor stripe laser diodes 714. The base substrate 700 providesmechanical support and registration for the laser diodes 702, the lenses704, the modulators 706, the lenses 708, the harmonic converters 710 andthe micro-optic lens 712.

In a first preferred embodiment of the red laser array 104, themonolithic array of semiconductor stripe laser diodes 702 are grown fromthe AlGaInP quaternary III-V semiconductor material system to directlyemit the radiation of the desired red color. In this embodiment, themodulation of the output laser beam of each stripe diode is imposed bydirectly modulating the drive current at each diode. The modulatedradiation from each of the semiconductor stripe laser diodes of lineararray 702 is then immediately collimated by the micro optic lens 712 toform the linear array of red output beamlets of the red primary colorarray source. In this preferred embodiment the micro optical lenses 704,modulator 706, the electro-optic micro-optic lenses 708 and the harmonicconverters 710 are omitted.

In a second preferred embodiment of the red laser array 104, radiationfrom the linear array of AlGaInP red stripe diodes 702 is modulated uponpassing through the linear array of electro-optic modulators 706, andimmediately collimating the modulated linear array of output beamletsusing linear lens array 712; As in the first preferred embodiment themicro-optic lenses 708 and the harmonic converters 710 are omitted.

In a third preferred embodiment of the red laser array 104, themonolithic array of semiconductor stripe laser diodes 702 is grown fromthe InGaAsP quaternary (or InGaAs; InGaAs ternary) III-V semiconductormaterial to emit light at twice the wavelengths of the desired red(green; blue) primary color, for example, at an infrared wavelength of1300 nm for red (1040 nm for green; 960 nm for blue). In thisembodiment, the modulation of the output of each stripe diode is imposedby directly modulating the diode drive current at each of the diodes702. The modulated radiation from each of the semiconductor stripe laserdiodes 702 is then immediately coupled to the linear array of stripenonlinear harmonic converters 710 via the linear array of micro-opticcoupling lenses 708. The linear arrays of stripe nonlinear harmonicconverters for red, green, and blue primary color array sources comprisequasi-phased-matched waveguides grown, for example, from the LiNbO₃,LiTaO₃, KTP, KNbO₃ material systems. The linear array of red (green;blue) modulated output beamlets from the nonlinear converter array isthen collimated by linear lens array 712.

In a fourth preferred embodiment, a variant of the third preferredembodiment, the modulation of the infrared radiation from the array ofsemiconductor stripe laser diodes 702 is achieved by passing it throughthe linear array of electro-optic modulators 706 prior to passing itthrough the integrated linear array of stripe nonlinear harmonicconverters 710 and the linear array of output collimating lenses 712.The linear array of electro-optic modulators 706 consists of NMach-Zehnder interferometers grown, for example, from the LiTaO₃,LiNbO₃, KTP material systems. In further detail, FIG. 6B illustrates aset of integrated electro-optic modulators 714, 716 and 718 followed bya nonlinear harmonic converter 720, 722 and 724 respectively. Althoughnot illustrated in FIG. 6A, there is one electro-optic harmonicconverter for each of laser diodes 702.

Referring now to FIG. 6C, when each of the laser diodes 702 which ismodulated directly by varying the current to such diode(s), theelectro-optic modulator 706 is not required. Instead, the harmonicconverters 710 are utilized as illustrated in detail in FIG. 6C. Inparticular, these converters 710 consist of a non-integrated array.

Referring now to FIGS. 7A, 7B and 7C, one preferred embodiment of thewhite light linear array source 100 of FIG. 1 is illustrated in greaterdetail. The red, green and blue laser linear arrays 104, 106, and 108respectively are shown, along with the optical combining mirrors 804,806 and 808 that are mounted onto a base plate 800 that is cast from alightweight material such as aluminum or magnesium. The base plate 800functions as a heat sink for the laser arrays 104, 106 and 108. The baseplate 800 further provides datums for registration of the arrays 104,106 and 108 to the base plate 800. An optical combiner 802 includes themirror 804 and the pair of dichroic mirrors 806 and 808. The opticalcombiner 802 combines corresponding 1-to-N collimated beamlets 110, 112and 114 from each of the linear arrays source 104, 106 and 108 into thesingle linear array of N parallel-traveling, collimated white lightbeamlets 102. Each of the three primary color linear array sources 104,106 and 108 is fabricated as an integrated linear array subassembly asshown in FIGS. 7A, 7B, 7C and 7C.

Referring now to FIG. 7B there is shown a front view of the white lightlaser array source 100 of FIG. 1. FIG. 7C illustrates the combination ofa set of electro-optic modulators (of Mach-Zehnder interferometer type)810, 812 and 814 and their associated integrated harmonic converters816, 818 and 820 respectively.

FIG. 7C corresponds to FIG. 6B.

Referring now to FIG. 7D, an end view of the harmonic converters 710 ofFIG. 6A is shown.

FIG. 7D corresponds to FIG. 6C.

A second preferred embodiment of the white light linear array isdescribed further herein with reference to FIG. 8C.

Data Processing system

FIGS. 8A, 8B, 8C and 8D illustrate overall data flow and basic rastergeneration of the data processing system 200 of FIG. 1, within the imageprojection system 10. The video signal 201 enters the video inputconverter 202, and whether the signal is standard NTSC, RGB component,or VGA computer, in all cases the signal is converted to 8-bit digitalRGB video, as three separate data streams. The video input converter 202includes an analog-to-digital converter 900, a phase lock loop 902 and acomposite component decoder 904. Such video converters are well known inthe art and may be constructed from commercially available chip sets. Inparticular a Philips Semiconductor TDA8708 analog-to-digital convertertogether with a Philips Semiconductor SAA 7191 luma, chromaprocessor/sync and clock processor and a Philips SAA 7197 clockgenerator circuit operate to separate a analog composite video signalinto digital luminance, chrominance, horizontal and vertical signals. ATRW TMC2272 digital colorspace converter/corrector converts thesedigital signals and provides separate red, green and blue digitaloutputs. Referring now to both FIGS. 8A and 8B, the red, green and bluedigital signals then pass into a memory 906 which is used for horizontaltime base correction and as an input memory (only several lines needed)necessary for the resizing processor to operate in a zoom mode. Thestabilized red, green and blue digital data is clocked out on demandfrom a set of memories 908, 910 and 912 into an image resizing processor914 for data resolution translation to match the fixed resolution of thewhite light laser array source 100 and the optical scanning/projectionsystem 300. The image resizing processor 914 contains a set of separateprocessors 916, 918 and 920 for the red, green and blue componentsrespectively.

After being resized and remapped, the red, green and blue videocomponents are inputted into a memory store 922 where re-rasterizationinto 128 line swaths takes place. The memory store 922 contains a set ofseparate swath memory banks 924, 926 and 928 for the red, green and bluevideo components respectively. Referring now to both FIGS. 8B and 8C,after re-rasterization groups of scan line data (swaths) are read outfrom the memory store 922 in a parallel multiplexed format and providedto a pulse modulator IC bank 930 to form a pulse width modulated signalwhich represents the intensity of the video. Each binary pulse-signal,that represents the illumination of the RGB components along a scanline, is applied to the lasers. The pulse modulator IC bank 930 includesread only memory (ROM) that stores data to convert each eight bit streaminto a corresponding laser intensity. The pulse modulator IC bank 930includes a set of four pulse width modulators 932, 934, 936 and 938 forthe red video components, a set of four pulse width modulators 940, 942,944 and 948 for the green video component and a set of four pulse widthmodulators 950, 952, 954 and 956 for the blue video component. Since fora given power input, each laser diode can have a different outputintensity, the ROM can be modified so that each laser diode operateswithin a predetermined intensity range. A polygon mirror 306 and a flatmirror 302 provide horizontal and vertical deflection respectively ofeach swath.

Synchronization Timing Analysis

There are other standard signals that the various input modules generateand pass to the image projection system 10. They are the sampling clock,which is derived from the horizontal synchronization (sync), and asignal called FREF, Frame Reference. This is a signal that is usually anactive-low-going edge on the first pixel of active video, of the firstline, of the first field. All the other synchronizing signals can bederived from this one edge, including horizontal sync, vertical sync,blanking, and chrominance field reference.

A system control bus 960 is a bi-directional computer bus interface thatallows control and setup preference data to be transferred to go betweena system control microprocessor 962 and the various subsystems of theimage projection system 10. In particular the system controlmicroprocessor 962 responds to an interrupt from an input device (suchas an external computer), reads the corresponding input value, stores ita RAM 964, checks a ROM 966 for information regarding all the correctdestinations necessary for executing the values changes correctly, andthen performs a write function to all the destinations in sequence.

A system timing generator 968 generates all synchronization signalsneeded by the image projection system 10 for data exchange, video datasynchronization between all sub-systems, phase lock, encoding anddecoding of multiplexed signals, and direct modulation sub-pixel highspeed clock references.

System Control Bus

In further detail, the system control bus 960 is a bi-directionalcomputer bus interface. Using an NTSC video signal as an example, theimage projection system 10 must be able to control the amount of hue,saturation, brightness, and contrast in the same way a person usuallyadjusts a home CRT video monitor for preferences to have the picture to"look" right. In one embodiment of the present invention, valuescorresponding to specific amounts of hue, saturation, brightness andcontrast could all be pre-set values that are stored in a ROM/RAM 961allowing an operator to set-up either externally or from a front panelof the image projection system 10. Information provided from the userpasses through the system over the control bus 960 to the appropriatesubsystem.

In the preferred embodiment of the invention all of the subsystems ofthe image projection system 10 have the same feature bus interface, soany plug-in can send and receive the same type of data. Each subsystemhas a unique destination address, so a user could select any subsystemas the source from a remote control or from the projector front panel.The system control bus 960 is an operating information bus that connectsbetween all the different parts of the image projection system 10 aswell as to an external host computer. In the preferred embodiment of theinvention, the host computer is an IBM AT type with a serial I/O(RS-232) port.

Video Input Converter

NTSC RS-170A

With reference now to the video input converter 202, NTSC RS-170A, isbroadcast to U.S. households or output from VHS tape recorders orvideodisc players. As specified in FIG. 10C, an important specificationfor NTSC video is that the aspect ratio is 4:3, which is not a widescreen aspect ratio. In the preferred embodiment of the invention, aNTSC interlaced video signal is digitized to a resolution of 768 pixelshorizontally across a line, for high quality representation, and between480 and 484 active vertical lines. The chrominance signal is encodedseparately from the luminance signal and is lower in resolution. Becauseof known artifacts in the digitized video signal, digital imageenhancement, which is well known in the art, may be utilized to improvepicture quality for a large projected image. Alternatively, digitalsignals may be provided directly to the composite/component decoder 904.In such an instance, all signals with the image projection system 10 aredigital.

With reference now to the video input converter 202, a typical videodecoder for a broadcast NTSC signal has an input which accepts acomposite signal that contains color and luminance information encodedtogether with a sync signal. Prior to decoding, the sync signal is firststripped off of the composite analog signal. The horizontal sync signalis used to synthesize a sampling clock, as the reference pulse for thephase lock loop 902 as it occurs once every horizontal line. Next thecomposite video signal (luma and chroma) is digitized by theanalog-to-digital converter 900 and the chroma-luminance separation isperformed digitally by the composite/component decoder 904. Decodingdigitally is much cleaner than analog decoders that are now used inconsumer TV receivers. With the analog method, filters are used toseparate the chrominance components from the composite signal. Suchanalog filters introduce distortion and reduce overall signal bandwidth.Luminance and chrominance samples decoded from the composite digitalsignal are applied to a digital matrix (such as the TRW TMC2272 DigitalColorspace Converter Corrector) to obtain a RGB color space signal. Thevideo passes through the image projection system 10 in the RGB form at.

In the preferred embodiment of the invention, an NTSC analog compositevideo signal is provided to the video input converter 202, and imagedata is supplied by the output of the video input converter 202 to thesubsystems of the image projection system 10 in RGB color space. RGB isan equal luminance-chrominance-resolution format, meaning that luminancechanges and color changes can both occur at the same rate in terms ofbandwidth. A NTSC analog composite signal has luminance (Y) and colordifference signals (U and V), however, NTSC is not an equal resolutionformat. The luminance (Y) typically has 4 MHz resolution, the colordifference signals (U, V) usually have 1.5 and about 0.5 MHz resolutionrespectively. Thus, NTSC saves bandwidth by carrying less colorinformation. Video in the form of graphics and high resolution text,however, is all equal resolution. Within the video input connector 202the luma- and color-difference signals are converted to RGB, in order tomore easily display equal resolution video sources.

1050/29.9 and HDTV 1125/30

With reference now to FIGS. 8A-8D, 10A and 10B, a second preferredembodiment of the video input converter 202 is described. The secondpreferred embodiment of the video input converter 202 is configured toprocess HDTV video signals, such as the 1050 2:1 NBC proposed standarddetailed in FIG. 10B and the 1125 SMPTE 240M standard detailed in FIG.10A. Video signals conforming to either of these standards are alreadyin RGB form, usually on three separate cables. Thus, theanalog-to-digital converter 900 includes three separateanalog-to-digital converters. By utilizing separate analog-to-digitalconverters, cross-contamination is minimized. This results in threepaths, 8 bits each of R, G, and B. The sync and clock signals aregenerated for all standards in the same way as for NTSC signals.

Usually the HDTV standards signals carry H and V separately, sometimescomposite, and often on a separate wire. The HDTV standard of FIG. 10Autilizes a "tri-level sync." Although difficult to detect, andvulnerable to noise, it is a bi-level type of standard that under normalconditions is easily decoded as is well known in the art.

In contrast to the first preferred embodiment of the video inputconverter 202, the second preferred embodiment (for HDTV) is actuallysimpler since the components are in a separate form and theanalog-to-digital converters simply need to run at a higher clock rate.The phase lock loop 902 insures that the sampling clock runs at a higherclock rate.

A third preferred embodiment of the video input converter 202 isconfigured to process VGA computer graphics signals. VGA graphicsinformation is typically stored in the RAM on a display card within acomputer in a look-up table mode. This means that between 8 and 16 bits,up to 24 bits on a digital signal bus (within the computer) is used asan address of a location in a RAM. The address in the RAM is programmedwith any one of millions of color possibilities, but only some limitednumber available at one time. This type of scheme is used in graphics toallow any set of color palettes.

Given the limited number of color possibilities available within aparticular color palette, the colors loaded into memory must becarefully selected to avoid an unnatural looking display. Using analogVGA as input to the video converter 202 would require redigitizing apreviously digital signal (data) resulting in degradation from theoriginal digital signal. Therefore, in this third preferred embodimentof the video input converter 202, the bit stream from a VGA feature busconnector of the computer is used as a clean source. Using this signalas the address of a look-up table, which would be the inverse of thecolor table data normally found on the VGA card, provides RGB directlyin digital from, and is compatible with the RGB format utilized by theimage projection system 10.

In further detail, the look-up table is loaded with the same values asin the VGA card within the computer. The VGA feature bus connector andthe computer's serial interface connector is used with a softwareinterface routine to download the color table data from the computerinto the image projection system 10. In the preferred embodiment of theinvention, a standard cable with a pair of D9 type connectors for serialoutput links to an AT type computer with a VGA interface card in theimage projection system 10. This yields identical colors on both adisplay connected to a computer and on the screen 400 of the imageprojection system 10. Clock, horizontal and vertical drive (sync)signals originate directly in digital form on the VGA feature connector.These signals are utilized to generate the input clock signal and FREF.

Time Base Corrector Memory

The preferred embodiment of the invention utilizes time base correctionin order to more accurately display video signals originating from videotape or other video sources. The time base of such signals is altered bytheir particular reproduction system because their reproduced videosignals have jitter generated as the tape moves across the head andbecause of minor variations in tape speed. Furthermore, because tapeheads are not perfectly round, there is uneven stretch in the tapethereby causing minor shifts in each horizontal line. And even during asingle line there are variations in tape speed sufficiently great toadversely affect the chroma and luma characteristics of the videosignal. In home TV receivers, the deflection is designed to overscan thevideo raster larger than the size of the tube. As a consequence, theuser never actually sees the ragged edge of the video. Some part of itis actually hidden off the screen by the plastic bezel plate placed overthe screen. If there is a minor shift in horizontal lines, the raggededge is hidden. This shift degrades the overall image, verticalresolution and causes improper color signal decoding. However, mosttelevision viewers remain oblivious to such fidelity problems.

With a projector displaying a large image, however, such minor shifts inhorizontal lines are more noticeable. For example, in order to show anentire image on a huge rectangular screen, the raster cannot beoverscanned. Instead, the image is horizontally re-aligned. Modern TV'suse what is known as a "fast horizontal AFC" typically 0.5 millisecond(as compared with 5-7 milliseconds found in older sets). Using a smalltime constant in a horizontal oscillator phase lock loop allows thescanning system to `instantaneously` correct for minor changes inhorizontal timing that the ragged edges are partially corrected.However, such a technique is not useful with an electromechanicalscanning system (as opposed to electromagnetic) since anelectromechanical scanning system has a significant mass which isdifficult to vary make such corrections.

A similar process of disturbing the time base is often used as a copyguard protection method to protect against unauthorized home VCRrecording. The headwheel in the VCR is much like the scanning polygonmirror. Video recordings that contain copy guard protection are oftenpre-distorted with a small amount of horizontal and vertical jitter thata TV receiver sync scanning circuit can fast track the error, but aVCR's headwheel cannot. Thus, a video time base corrector is utilizedfor the preferred embodiment of the present invention.

With reference now to FIG. 8B, the time base corrector and buffer memory906 is described in further detail. The time base corrector and buffermemory 906 sample a few scan lines and read them into memory withcontrol information. Digital logic contained in the time base correctorand buffer memory 906 determines that the horizontal sync has deviatedfrom a standard synthesized internal horizontal sync, and in responsethe time base corrector section re-shifts the lines by some minuteamount so that they will all line up again. The lines are then read outof the buffer memory section in perfect synchronism for display as aperfect raster.

Image Resizing

The image projection system 10 of the present invention displays avariety of image formats. This places a tremendous burden on thescanning electronics because there are different numbers of pixels perlines, and different numbers of lines, different blanking times betweenretrace. To display all raster formats with the restrictions imposed bya predetermined number of laser light sources is impractical. Turningoff different combinations of laser light sources to obtain a fully litraster causes uneven line spacing. There will always be some multiplesof frequencies and/or scan lines that an optical scanning system cannotaccommodate.

In order to overcome this problem, the image projection system of thepresent invention uses the image resizing processor 916 to convertdifferent numbers of pixels per line and different numbers of scan linesand convert them into one common resolution. As graphically illustratedin FIG. 9, with this method, it becomes possible to optimize the imageprojection system 10 for a predetermined image size. In addition, theconversion method utilized in the present invention corrects for imagesexisting in different aspect ratios. If an optical scanning projectionsystem is configured to produce a specific aspect ratio, for videousually between 16:9 and 4:3, it is necessary for some additionalhorizontal shrinking and zooming, depending on which operation isnecessary to correct the aspect ratio raster.

In further detail, the image resizing processor 914 performs two imageresolution transformations, one for resolution matching and one foraspect correction.

The image resizing processor 914 receives image input at any number ofpixels per line and any number of lines and performs an interpolationfunction in the digital domain to thereby yield more or fewer pixels perline and more or less lines per frame. The image input is converted to acommon format for the scanning/display generation for a fixed number oflasers in the array and a mirror with a fixed number of facets. In thepreferred embodiment of the invention, the image resizing processor 914converts all inputs to a common format of 1280 pixels by 1280 lineswhich is based upon 128 laser diodes in each laser array.

In the preferred embodiment of the invention, the image resizingprocessor 914 performs fractional re-scaling, horizontal and/orvertical, independently done in either dimension, horizontally andvertically. Any image signal can be matched to the fixed 1280×1280format. In operation, complex interpolation and variable bandwidthfilter algorithms perform resizing of image data in real time at highspeed.

The image resizing processor 914 accepts control from the system controlbus 960, the same bus described with respect to the video inputconverter 202 and image projection system 10. The image resizingprocessor 914 loads line and pixel parameters, based upon requiredresizing factors obtained from an internal table that contains valuescorresponding to each of the various standards. This results in thecorrect aspect ratio as well as the correct number of lines and pixelsper line. Image resizing techniques that are suitable for use inconnection with the preferred embodiment of the invention are disclosedin the paper entitled "Video Resizing--how to make bigger/smaller imagethe best it can be|" by James H. Arbeiter, Proceedings, ElectronicImaging International, Sep. 29-Oct. 2, 1992, Hynes Convention Center,Boston, Mass., which paper is incorporated herein by reference.

There are a variety of vertical frequencies for video signals. There is59.9Hz for NTSC and the proposed 1050 HD standard; there is1125/60--which is actually 1125/30 because it is a 30 Hz frame rate-andthere is VGA computer graphics, that can vary vertically between 40 and70 Hz.

For the image projection system 10 to accommodate various vertical scanrates, the polygon motor is rotated at different speeds, and the flatmirror is deflected so that it provides vertical deflection at the samerate as that of the input video signal. Whatever image signal isdisplayed, the scanning optics remain the same, because it is always thesame amount of data, input re-sized to fixed scanning resolution, thedifference is in data rate only. A different vertical scanning raterelates to scanning out the whole field or frame faster or slower. Thisconcept can be thought of as the same raster going on the screen, it isjust scanned out a little faster or slower, based on the vertical rate,which is the field or frame update rate.

The image resizing process, coupled with the variable speeds of thepolygon drive motor and the vertical deflection galvanometer and itsassociated control electronics 310 provides a method to handle any imageformat that is input to the image projection system 10. All thenecessary parameters can be pre-coded into ROM tables in order tounburden the system from having to perform the computations necessary toobtain them.

Swath Memory Banks

In the preferred embodiment of the invention, sufficient brightness isobtained by scanning many lines in parallel.

Since all current video standards are in CRT raster format, meaning asingle data stream for a single beam which scans back and forth, thepresent invention includes a method of converting from a single beaminput format to a raster scanning of multiple laser beams scanning outsimultaneously.

In accordance with the present invention, all of the lines needed forthe parallel scan are stored in the memories 924, 926 and 928 and readout to produce parallel scanned lines. The first pixel for all the linesis read from the memory first and then the second pixel for all linesand so on at 1/N speed, where N=number of parallel lines. All the laserdiodes are active at the same time. One preferred method for performingthe function is to use two memories. A first memory stores a group of Nlines while a second memory outputs a group of N lines in parallel. Thenthey "ping-pong" back and forth. Video is read into either memory, theaddresses sequentially incremented, and at the output the video is readout in a line-parallel fashion.

It is almost impractical to use 128 8-bit paths going out of the memory.A method for alleviating this problem would be to read out from thememory in a different order, meaning read out the N pixels for the Nlines, then N pixels of N+1 lines. This is called a multiplexed formatwhere data appears sequentially on a single wire and the order of thesequence is known and decoded at the destination. Since the data goesout N times as slowly, N pixels can be read out in the same amount oftime and then each one shown them as the first pixel on all parallelsources. The data rate going into either memory is the same as the datarate going out. If we had different data rates, the memory would eitheroverflow or become exhausted.

Pulse Width Modulators

In the preferred embodiment of the invention, the image projectionsystem 10 uses 128 lines scanned out in parallel. With three (R, G, B)diodes per pixel, this results in a total of 384 active video channels.These channels originate as 384 equivalent (multiplexed) data streamsfrom scan-converting frame stores 924, 926 and 928. In the preferredembodiment of the invention, each channel uses 8-bit equivalentresolution. Each such digital signal is converted to an analog signal inorder to drive the laser diodes to reproduce the time varying pixelamplitude (and color) for each of the 128 scan lines. 384digital-to-analog converters in any system is an extremely large numberof devices, requiring large PC board real estate, tedious calibration,and linearized driver electronics of sufficient power and bandwidth.

The preferred embodiment of the present invention uses pulse-widthmodulation to provide a full power current source for each laser with atime varying pulse train (duty cycle), so that the average powerdelivered to any diode over the pixel time will correspond to light fromthe diode at specific intensity. As illustrated in FIG. 11, this wouldbe the same exact amplitude that the D/A converter would produce for agiven 8-bit value, that in fact is the R, G, B intensities for video fora given pixel. This is advantageous for several reasons. Switch-modeelectronics eliminates the need for D/A converters, highly filteredpower supplies, linearized driver electronics, and costly setup andcalibration. Switch-mode logic uses less power than its analogcounterpart, since there is little power dissipated in outputtransistors themselves as they are either fully on or fully off.Although specific examples of pulses for generating specified intensitylevels are illustrated in FIG. 11, different numbers, timing andamplitude of each of the pulses may be utilized to deliver apredetermined amount of energy to each laser diode over a predeterminedperiod to thereby establish the (perceived) intensity of the output ofsuch laser diode. Alternatively, such pulses can drive Mach-Zehnderinterferometer modulators to control the intensity of each beam.

Switch-mode pulse code modulation (PCM) is normally not applied todigital video systems. The reason is that for 8-bit resolution (256levels of intensity) and 4 MHz video bandwidth, the switching rate wouldhave to be extremely fast. For example, if a pixel needed to be minimumintensity, or 1/256 as bright as full intensity (256 levels), and ifresponse were linear, a reasonable assumption might be that a pulse thatwas full on for 1/256 of the overall pixel time would be needed. Thatwould require a clock 256 times as fast as the pixel clock used fordigitizing the input video data stream. Most drivers could not switchsufficiently fast for this application and would become slow-ratelimited. In addition, the digital logic to generate such fast pulsetrains does not exist in any off-the-shelf or cost effective form.

However, the image projection system 10 of the present invention scansout swathes of line-slowed-down video. In the case of 128 swathes, theline time is 128 times longer. The switch rate drops by almost a factorof 128, that is within the normal operating range for CMOS type IClogic. This range is very reasonable for operation of a switch-modedriver. For pulse width modulation, the amount of light energy resultingfrom the duration of some number of pulses is proportional to theamplitudes of each video sample (pixel).

In order to achieve performance acceptable to most viewers it isnecessary to have more than enough on-off cycles during one pixel timeto produce the minimum of intensity values for good quality imagereproduction. Because the image projection system 10 has such a largedisplay and excellent beam/optics, and the human eye is extremelysensitive to grey level resolution, and in the preferred embodiment ofthe invention, 256 grey levels are utilized instead of the 128 levelsillustrated in FIG. 11. The modulation used will at any sampling instantto produce a specific pulse duration, based on an 8-bit intensity code,to generate the amplitude value of the baseband signal. For any analogsignal the pulse width modulation (PWM) varies linearly between the twoextremes of non-intensity to full-intensity. The widest cumulative pulsetime represents the maximum energy delivered and the narrowestcumulative pulse time represents the minimum energy, or minimumintensity.

The duration of the pulse varies as a function of the amplitude of theimage signal. The eye has the ability to integrate modulated lightpulses into an averaged perceived value. However, it may be desirable touse an integrator to smooth the sharp step, inherent in switchedoutputs, to produce a more average value. Alternatively, using a finerpulse step increment may eliminate the need for a post filter. Thisscheme requires fewer components than analog integrators. Also, pulsemodulation schemes can scale over wide frequency ranges, whereas theanalog components are generally specified for only one sample frequency.

Using this pulse modulation method simplifies the amount of analogelectronics and wired interconnects in the image projection system 10.In addition, many PCM units could be placed on a single IC device(typically 32 modules).

In the embodiment shown in FIG. 8C, outputs from the red laser array104, the green laser array 106 and the blue laser array 108 are combinedusing different combining optics than in the embodiment shown in FIG.7A-7D. In particular, parallel beams of primary color are reflected by amirror 951, parallel beams of a second primary color are reflected by amirror 953, and parallel beams of a third primary color are directed toa combining cube 955 that operates to combine corresponding parallelbeams of each primary color.

Raster Generation and Servo

Horizontal Deflection

In the preferred embodiment of the invention, the horizontal deflectionof the laser swath is provided by the rotating polygon mirror 306. Thedrive motor 308 is locked to the incoming horizontal drive signal whichis synchronized with the start of each swath (horizontal line group)read out under control of the swath memory banks 922. Optical feedbackfor a control system is provided by a line 972 scribed on the top of thepolygon mirror 306 which aligns with the facet edge. Each facet is usedto deflect one swath. Thus, the polygon facet edge signal derived fromthe scribed line and the incoming horizontal drive serve as inputs tothe motor servo phase locked loop 970. Although FIG. 8D illustrates apolygon mirror 306 having a total of nine facets, since the polygonmirror only provides horizontal deflection, the number of facets is notcritical to the design of the system. In particular, if it takes eightswaths to make a complete 1024 line raster, correspondingly it takeseight facets to make one frame. The vertical blanking time (time for theinterlace galvanometer to reset) is accommodated by skipping an integernumber of facets.

Vertical Deflection

In the preferred embodiment of the invention, vertical deflection isprovided by a galvanometer 304 having an integral mirror 304. The mirror304 moves in a continuous and linear fashion during each active frametime. Since the mirror 304 cannot move instantaneously or in discretesteps, it therefore moves during the entire active swath time. At theend of a swath and after horizontal blanking, the amount of verticaldeflection is precisely enough so that line one of swath number twobegins underneath the line 128 of swath number one. This causes theraster to tilt by an amount of one swath's height, or 28 scan lines.This tilt is removed optically before the raster is projected on thescreen. The amount of time needed for vertical retrace is estimated tobe between ten and thirty percent of the total frame time. The syncblanking time of the input video and graphics sources will varydepending on the display standard which they conform to. In any systemwith a rotating polygon mirror 306 there will always be some discretenumber of facets to skip over one frame time and therefore a syncblanking ratio can be established. If the frame time is the same for theinput video as it is the scanned out image, then the data can be readout from the frame store slightly slower or faster to meet the integercriteria. As previously described with respect to FIGS. 1, 4 and 5, agalvanometer may be used to provide the capability to display interlacedformats.

Optical Scanning Protection System

FIG. 12 illustrates a schematic layout of one embodiment 1200 of theoptical scanning/projection system 300 of FIG. 1. This embodiment 1200utilizes a conventional rotating polygon mirror 1202 and thegalvanometer deflector mirror 302 to raster successive swath scansvertically down the screen. An appropriate prescan collimator 1204, avertical fold mirror 1206, a horizontal fold mirror 1208 and a 1:1 relaysystem 1210 are utilized to image the output of the white light laserarray source 100 of FIG. 1 at the facets of the rotating polygon mirror1202. The projection optics 312 relay this image to the projectionscreen 400. In the preferred embodiment of the invention, the prescancollimator 1204 is a spherical mirror. The 1:1 relay 1210 consist of afirst concentric spherical mirror 1212 and a second spherical mirror1214, both mirrors being nearly concentric. The mirrors 1212 and 1214are designed to operate within a finite telocentric field. The functionsof the relay 1210 have been inverted to thereby image the collimatedfield from pupil to pupil with unity magnification.

Referring now to FIG. 13, another embodiment 1300 of the opticalscanning/projection system 300 of FIG. 1 is shown. This embodiment 1300differs from the embodiment 1200 of FIG. 12 in that the rotating rightpolygon mirror 1202 of FIG. 12 is replaced with a tilted facet rotatingpolygon mirror 1302 and the galvanometer mirror 302 is replaced with afixed fold mirror 1304. In this embodiment 1300, the successively angledsurfaces of the rotating polygon 1302 control the successive swath scansof the output from the white light laser array source 100 of FIG. 1.Because of the successively angled surfaces of the rotating polygonmirror 1302, the successive swaths are vertically rastered down thescreen 400 thereby eliminating the need for a galvanometer mirror 302and its integral galvanometer 304 as shown in FIG. 1.

In FIG. 13 collimated output from the white light laser array source 100is directed to the polygon mirror 1302 via a pre-scan collimator 1301,the fixed fold mirror 1304, a vertical fold mirror 1305, a polarizingbeamsplitter 1306 (used in reflection) a quarter waveplate 1308 and ahorizontal fold mirror 1309. The angled polygon 1302 scans 10 swaths ofa 128 line array to thereby provide a 1280 line field. This scan fieldis split from the input to the polygon mirror 1302 by passing throughquarter waveplate 1308 a second time (to complete a 90° rotation of thepolarization) and transmitted through the polarizing beam splitter 1306.An F-theta scan lens 1310 creates an intermediate image that isdisplayed onto the screen 400 by a projection lens 1312. The geometry ofthe angled polygon mirror 1302 must be selected to balance two competingraster errors. The optical scan angle produced by one facet must besufficiently small to minimize swath mismatch, but sufficiently large tominimize the raster cross-scan displacement caused by facet pyramidalangle error plus the effects of wobble of the angled polygon mirror.

While the embodiments of the various aspects of the present inventionthat have been described are the preferred implementation, those skilledin the art will understand that variations thereof may also be possible.Therefore, the invention is entitled to protection within the full scopeof the appended claims.

We claim:
 1. An image projection apparatus, comprising:a plurality ofprimary wavelength light sources for generating a plurality of paralleltraveling light beamlets, the plurality of primary wavelength lightsources including at least one non-linear harmonic converter formultiplying the frequency of light beamlets generated by a linear arrayof semiconductor laser diodes; means for modulating the paralleltraveling light beamlets; and a plurality of rotating reflectivesurfaces for scanning and projecting the modulated parallel travelinglight beamlets onto an image receptor, each successive rotatingreflective surface adjacent to and skewed from a preceding rotatingreflective surface, all of the plurality of rotating reflective surfacesrotationally driven at the same angular velocity.
 2. The imageprojection apparatus of claim 1, further comprising:a galvanometeroperative to deflect each of the parallel traveling light beamlets toprovide at least one interlaced field within a frame.
 3. An imageprojection apparatus, comprising:a plurality of primary wavelength lightsources for generating a plurality of parallel traveling light beamlets,each primary wavelength light source including a linear array ofsemiconductor laser diodes for generating parallel traveling lightbeamlets, the plurality of primary wavelength light sources including atleast one non-linear harmonic converter for multiplying the frequency oflight beamlets generated by the linear array of semiconductor laserdiodes; means for modulating the parallel traveling light beamlets; andmeans for scanning and projecting the modulated parallel traveling lightbeamlets to generate pixels onto an image receptor.
 4. The imageprojection apparatus of claim 3, wherein the plurality of primarywavelength light sources further comprises:a red light linear array forgenerating a plurality of red light beamlets; a blue light linear arrayfor generating a plurality of blue light beamlets; a green light lineararray for generating a plurality of green light beamlets; and means forcombining the red, green and blue beamlets into parallel traveling lightbeams.
 5. The image projection apparatus of claim 4, wherein said meansfor combining further comprises:a mirror for reflecting each beamlet ofone of the red, green and blue plurality of light beamlets; a firstdichroic filter for transmitting each beamlet of the plurality of lightbeamlets reflected by the mirror and spatially combining each suchbeamlet with each corresponding beamlet of one of the two remainingpluralities of light beamlets; and a second dichroic filter forspatially combining each combined beamlet from the first dichroic filterwith each corresponding beamlet of the one remaining plurality of lightbeamlets.
 6. The image projection apparatus of claim 3, wherein:acomplete image projected onto an image receptor is formed by a singlescan of parallel traveling light beamlets.
 7. The image projectionapparatus of claim 3, wherein the means for scanning and projecting themodulated parallel traveling light beamlets scans and projects a fixedpreselected number of pixels on the image receptor independent of aninput image format, and further comprises:means for receiving a signalin the input image format, the signal containing image data the imagedata corresponding to a first number of pixels; and remapping means forselecting from the first number of pixels a second number of pixels asat least a portion of the fixed preselected number of pixels forscanning and projection, the remapping means including interpolationmeans for generating additional pixels from the image data when thefixed preselected number of pixels exceeds the first number of pixels.8. The image projection apparatus of claim 7, wherein said means forremapping comprises:a serial to parallel converter.
 9. The imageprojection apparatus of claim 3, wherein said means for scanning andprojecting further comprises:at least one lens; and at least one mirror.10. The image projection apparatus of claim 3, further comprising:agalvanometer operative to deflect the modulated parallel traveling lightbeamlets.
 11. An image projection apparatus, comprising:a plurality ofprimary wavelength light sources for generating a plurality of paralleltraveling light beamlets, the plurality of primary wavelength lightsources including at least one non-linear harmonic converter formultiplying the frequency of light beamlets generated by a linear arrayof semiconductor laser diodes; a pulse width modulator for varying theamount of energy emitted from each primary wavelength light source; andmeans for scanning and projecting the modulated parallel traveling lightbeamlets to generate pixels on an image receptor.
 12. A method ofprojecting an image, comprising the steps of:providing a plurality ofparallel traveling light beamlets of a first primary color; providing aplurality of parallel traveling light beamlets of a second primarycolor; providing a plurality of parallel traveling light beamlets of athird primary color by multiplying with at least one non-linear harmonicconverter the frequency of light beamlets generated by a linear array ofsemiconductor laser diodes; modulating the plurality of paralleltraveling light beamlets; combining the modulated parallel travelinglight beamlets to form a plurality of modulated parallel white lightbeamlets; reflecting the modulated parallel white beamlets from aplurality of rotating reflective surfaces onto an image receptor, eachsuccessive rotating reflective surface adjacent to and skewed from apreceding rotating reflective surface; and rotationally driving all ofthe plurality of rotating reflective surfaces at the same angularvelocity.
 13. The method of claim 12 wherein the image receptor is aneye, further comprising the step of:reflecting the modulated parallelwhite beamlets from the plurality of rotating reflective surfacesdirectly into the eye.
 14. An image projection apparatus,comprising:video processing means for receiving image data andgenerating digital red signals, digital green signals, digital bluesignals and timing signals representative of image data; a first laserarray for generating a plurality of parallel traveling beamlets of afirst primary color; a second laser array for generating a plurality ofparallel traveling beamlets of a second primary color; a third laserarray for generating a plurality of parallel traveling beamlets of athird primary color, the third laser array including at least onenon-linear harmonic converter for multiplying the frequency of lightbeamlets generated by a linear array of semiconductor laser diodes;means for combining the plurality of parallel traveling beamlets of thefirst, second and third primary colors to generate a plurality ofparallel traveling white light beamlets; means for digitally modulatingthe intensity of the beamlets of the first, second and third primarycolors in response to the digital signals; and means for scanning andprojecting the plurality of parallel white light beams across a screen.15. An image projection apparatus, comprising:means for receiving imagedata and generating digital luminance signals and timing signalsrepresentative of image data; a laser array for generating a pluralityof parallel traveling light beamlets, the laser array including at leastone non-linear harmonic converter for multiplying the frequency of lightbeamlets generated by a linear array of semiconductor laser diodes;means for pulse width modulating the intensity of the beamlets inresponse to the luminance signals; and means for scanning and projectingthe plurality of parallel traveling light beamlets onto an imagereceptor.
 16. A method of forming an image on a screen, comprising thesteps of:receiving image data representative of an image; generating aplurality of parallel traveling light beamlets by multiplying with atleast one non-linear harmonic converter the frequency of light beamletsgenerated by a linear array of semiconductor laser diodes; projectingthe plurality of parallel traveling light beamlets across a first areaof a screen; projecting the plurality of parallel traveling lightbeamlets across a second area of the screen; and pulse width modulatingthe plurality of parallel traveling light beamlets with the image data.17. A method of generating and scanning a plurality of paralleltraveling light beamlets across a screen, comprising the stepsof:generating a plurality of parallel traveling light beamlets bymultiplying with at least one non-linear harmonic converter thefrequency of light beamlets generated by a linear array of semiconductorlaser diodes; reflecting the plurality of parallel traveling lightbeamlets from a plurality of rotating reflective surfaces onto an imagereceptor, each successive rotating reflective surface adjacent to andskewed from a preceding rotating reflective surface; and rotationallydriving all of the plurality of rotating reflective surfaces at the sameangular velocity.
 18. An image projection apparatus,comprising:converter means for outputting a red digital signal, a greendigital signal and a blue digital signal in response to a video signalrepresentative of a color image; time base correction means forcorrecting timing errors of the red, green and blue digital signals;serial to parallel conversion means for generating sets of parallel datarepresentative of the color image; a plurality of primary wavelengthlight beamlet sources for generating a plurality of parallel travelingbeamlets, the plurality of primary wavelength light beamlet sourcesincluding at least one nonlinear harmonic converter for multiplying thefrequency of light beamlets generated by a linear array of semiconductorlaser diodes; modulation means for modulating the plurality of theparallel traveling beamlets in response to the parallel data; and meansfor scanning and projecting the modulated parallel traveling beamlets.19. The image projection apparatus of claim 18, further comprising:imageresizing means for spatially remapping the red, green and blue digitalsignals from a first format to a second format.
 20. The image projectionapparatus of claim 18, further comprising:a reflective screen.
 21. Theimage projection apparatus of claim 18, wherein the modulation meansfurther comprises:a pulse width modulator for generating groups ofpulses, each group of pulses having an energy content corresponding tothe luminance of at least one of the first, second and third primarycolors within one pixel of the color image.
 22. The image projectionapparatus of claim 18, wherein the modulation means comprises:at leastone Mach-Zehnder interferometer per beamlet.
 23. An image projectionapparatus, comprising:a plurality of light sources for generating aplurality of parallel traveling light beamlets, the plurality of lightsources including at least one non-linear harmonic converter formultiplying the frequency of light beamlets generated by a linear arrayof semiconductor laser diodes; means for pulse width modulating theparallel traveling light beamlets; and means for scanning and rasteringthe modulated parallel light beamlets to generate pixels onto an imagereceptor.
 24. An image projection apparatus, comprising:a plurality ofprimary wavelength light sources for generating a plurality of paralleltraveling light beamlets, the plurality of primary wavelength lightsources including at least one non-linear harmonic converter formultiplying the frequency of light beamlets generated by a linear arrayof semiconductor laser diodes; means for modulating the primarywavelength light sources; and a plurality of rotating reflectivesurfaces for scanning and projecting the modulated parallel travelinglight beamlets onto an image receptor, each successive rotatingreflective surface adjacent to and skewed from a preceding rotatingreflective surface, all of the plurality of rotating reflective surfacesrotationally driven at the same angular velocity.
 25. An imageprojection apparatus, comprising:a plurality of primary wavelength lightsources for generating a plurality of parallel traveling light beamlets,each primary wavelength light source including a linear array ofsemiconductor laser diodes for generating parallel traveling lightbeamlets, the plurality of primary wavelength light sources including atleast one non-linear harmonic converter for multiplying the frequency oflight beamlets generated by the linear array of semiconductor laserdiodes; means for modulating the primary wavelength light sources; andmeans for scanning and projecting the modulated parallel traveling lightbeamlets to generate pixels onto an image receptor.
 26. The imageprojection apparatus of claim 25, wherein the plurality of primarywavelength light sources further comprises:a red light linear array forgenerating a plurality of red light beamlets; a blue light linear arrayfor generating a plurality of blue light beamlets; a green light lineararray for generating a plurality of green light beamlets; and means forcombining the red, green and blue beamlets into parallel traveling lightbeams.
 27. The image projection apparatus of claim 26, wherein saidmeans for combining further comprises:a mirror for reflecting eachbeamlet of one of the red, green and blue plurality of light beamlets; afirst dichroic filter for transmitting each beamlet of the plurality oflight beamlets reflected by the mirror and spatially combining each suchbeamlet with each corresponding beamlet of one of the two remainingpluralities of light beamlets; and a second dichroic filter forspatially combining each combined beamlet from the first dichroic filterwith each corresponding beamlet of the one remaining plurality of lightbeamlets.
 28. The image projection apparatus of claim 25, wherein:acomplete image projected onto an image receptor is formed by a singlescan of parallel traveling light beamlets.
 29. The image projectionapparatus of claim 25, wherein the means for scanning and projecting themodulated parallel traveling light beamlets scans and projects a fixedpreselected number of pixels on the image receptor independent of aninput image format, and further comprises:means for receiving a signalin the first image format, the signal containing image data the imagedata corresponding to a first number of pixels; and remapping means forselecting from the first number of pixels a second number of pixels asat least a portion of the fixed preselected number of pixels forscanning and projection, the remapping means including interpolationmeans for generating additional pixels from the image data when thefixed preselected number of pixels exceeds the first number of pixels.30. The image projection apparatus of claim 29, wherein said means forremapping comprises:a serial to parallel converter.
 31. The imageprojection apparatus of claim 25, wherein said means for scanning andprojecting further comprises:at least one lens; and at least one mirror.32. The image projection apparatus of claim 25, further comprising:agalvanometer operative to deflect the modulated parallel traveling lightbeamlets.
 33. The image projection apparatus of claim 24, furthercomprising:a galvanometer operative to deflect each of the paralleltraveling light beamlets to provide at least one interlaced field withina frame.
 34. An image projection apparatus, comprising:converter meansfor outputting a red digital signal, a green digital signal and a bluedigital signal in response to a video signal representative of a colorimage; time base correction means for correcting timing errors of thered, green and blue digital signals; serial to parallel conversion meansfor generating sets of parallel data representative of the color image;a plurality of primary wavelength light beamlet sources for generating aplurality of parallel traveling beamlets, the plurality of primarywavelength light beamlet sources including at least one non-linearharmonic converter for multiplying the frequency of light beamletsgenerated by a linear array of semiconductor laser diodes; modulationmeans for modulating the primary wavelength light beamlet sources inresponse to the parallel data; and means for scanning and projecting themodulated parallel traveling beamlets.
 35. The image projectionapparatus of claim 34, further comprising:image resizing means forspatially remapping the red, green and blue digital signals from a firstformat to a second format.
 36. The image projection apparatus of claim34, further comprising:a reflective screen.
 37. The image projectionapparatus of claim 34, wherein the modulation means further comprises:apulse width modulator for generating groups of pulses, each group ofpulses having an energy content corresponding to the luminance of atleast one of the first, second and third primary colors within one pixelof the color image.
 38. An image projection apparatus, comprising:aplurality of light sources for generating a plurality of paralleltraveling light beamlets, the plurality of light sources including atleast one non-linear harmonic converter for multiplying the frequency oflight beamlets generated by a linear array of semiconductor laserdiodes; means for pulse width modulating the plurality of light sources;and means for scanning and rastering the modulated parallel lightbeamlets to generate pixels onto an image receptor.
 39. An imageprojection apparatus, comprising:a plurality of primary wavelength lightsources for generating a plurality of parallel traveling light beamlets,the plurality of primary wavelength light sources; means for modulatingeach parallel traveling light beamlet; at least one non-linear harmonicconverter for multiplying the frequency of at least one modulatedparallel traveling light beamlet; and a plurality of rotating reflectivesurfaces for scanning and projecting the modulated parallel travelinglight beamlets onto an image receptor, each successive rotatingreflective surface adjacent to and skewed from a preceding rotatingreflective surface, all of the plurality of rotating reflective surfacesrotationally driven at the same angular velocity.
 40. An imageprojection apparatus, comprising:a plurality of primary wavelength lightsources for generating a plurality of parallel traveling light beamlets,each primary wavelength light source including a linear array ofsemiconductor laser diodes for generating parallel traveling lightbeamlets; means for modulating each parallel traveling light beamlet; atleast one non-linear harmonic converter for multiplying the frequency ofat least one modulated parallel traveling light beamlet; and means forscanning and projecting the modulated parallel traveling light beamletsto generate pixels onto an image receptor.
 41. The image projectionapparatus of claim 40, wherein the plurality of primary wavelength lightsources further comprises:a red light linear array for generating aplurality of red light beamlets; a blue light linear array forgenerating a plurality of blue light beamlets; a green light lineararray for generating a plurality of green light beamlets; and means forcombining the red, green and blue beamlets into parallel traveling lightbeams.
 42. The image projection apparatus of claim 41, wherein saidmeans for combining further comprises:a mirror for reflecting eachbeamlet of one of the red, green and blue plurality of light beamlets; afirst dichroic filter for transmitting each beamlet of the plurality oflight beamlets reflected by the mirror and spatially combining each suchbeamlet with each corresponding beamlet of one of the two remainingpluralities of light beamlets; and a second dichroic filter forspatially combining each combined beamlet from the first dichroic filterwith each corresponding beamlet of the one remaining plurality of lightbeamlets.
 43. The image projection apparatus of claim 40, wherein:acomplete image projected onto an image receptor is formed by a singlescan of parallel traveling light beamlets.
 44. The image projectionapparatus of claim 40, wherein the means for scanning and projecting themodulated parallel traveling light beamlets scans and projects a fixedpreselected number of pixels on the image receptor independent of aninput image format, and further comprises:means for receiving a signalin the input image format, the signal containing image data the imagedata corresponding to a first number of pixels; and remapping means forselecting from the first number of pixels a second number of pixels asat least a portion of the fixed preselected number of pixels forscanning and projection, the remapping means including interpolationmeans for generating additional pixels from the image data when thefixed preselected number of pixels exceeds the first number of pixels.45. The image projection apparatus of claim 44, wherein said means forremapping comprises:a serial to parallel converter.
 46. The imageprojection apparatus of claim 40, wherein said means for scanning andprojecting further comprises:at least one lens; and at least one mirror.47. The image projection apparatus of claim 40, further comprising:agalvanometer operative to deflect the modulated parallel traveling lightbeamlets.
 48. The image projection apparatus of claim 39, furthercomprising:a galvanometer operative to deflect each of the paralleltraveling light beamlets to provide at least one interlaced field withina frame.
 49. A method of projecting an image, comprising the stepsof:providing a first plurality of parallel traveling light beamlets;providing a second plurality of parallel traveling light beamlets;providing a third plurality of parallel traveling light beamlets;modulating each of the plurality of parallel traveling light beamlets;multiplying with at least one non-linear harmonic converter thefrequency of at least one of the pluralities of parallel traveling lightbeamlets; combining the modulated parallel traveling light beamlets toform a plurality of modulated parallel white light beamlets; reflectingthe modulated parallel white beamlets from a plurality of rotatingreflective surfaces onto an image receptor, each successive rotatingreflective surface adjacent to and skewed from a preceding rotatingreflective surface; and rotationally driving all of the plurality ofrotating reflective surfaces at the same angular velocity.
 50. An imageprojection apparatus, comprising:converter means for outputting a reddigital signal, a green digital signal and a blue digital signal inresponse to a video signal representative of a color image; time basecorrection means for correcting timing errors of the red, green and bluedigital signals; serial to parallel conversion means for generating setsof parallel data representative of the color image; a plurality ofprimary wavelength light beamlet sources for generating a plurality ofparallel traveling beamlets; modulation means for modulating theplurality of the parallel traveling beamlets in response to the paralleldata; at least one non-linear harmonic converter for multiplying thefrequency of at least one modulated parallel traveling light beamlet;and means for scanning and projecting the modulated parallel travelingbeamlets.
 51. The image projection apparatus of claim 50, furthercomprising:image resizing means for spatially remapping the red, greenand blue digital signals from a first format to a second format.
 52. Theimage projection apparatus of claim 50, further comprising:a reflectivescreen.
 53. The image projection apparatus of claim 50, wherein themodulation means further comprises:a pulse width modulator forgenerating groups of pulses, each group of pulses having an energycontent corresponding to the luminance of at least one of the first,second and third primary colors within one pixel of the color image. 54.The image projection apparatus of claim 50, wherein the modulation meanscomprises:at least one Mach-Zehnder interferometer per beamlet.
 55. Animage projection apparatus, comprising:a plurality of primary wavelengthlight sources for generating a plurality of parallel traveling lightbeamlets, each primary wavelength light source including a linear arrayof semiconductor laser diodes for generating parallel traveling lightbeamlets, the plurality of primary wavelength light sources including atleast one non-linear harmonic converter for multiplying the frequency oflight beamlets generated by the linear array of semiconductor laserdiodes; means for projecting the plurality of parallel traveling lightbeamlets across a first area of a screen and across a second area of thesemen; and a pulse width modulator for modulating plurality of paralleltraveling light beamlets with image data.